Metals have long been used to form resistors, capacitors, and inductors—the three classical passive circuit elements in which geometry determines the principle behavior of the device. A fourth passive circuit element, the memristor, has generated significant recent interest due to its potential use in nanoscale logic and memory devices. Among the presently demonstrated memristors are those whose resistance depends on state variables such as coupled ionic and electronic conduction, phase transistions, redox reactions in organic semiconductors, and the configuration of molecular heterostructures.
U.S. Pat. No. 6,636,433 discloses an electronic device incorporating a memory core comprising either a material that can be electromigrated or a carbon nanotube having a hollow core holding a material that can be electromigrated which alters the overall conduction based on its position. To electromigrate the material, the approach disclosed in U.S. Pat. No. 6,636,433 is to utilize the Joule heating within the material or nanotube itself in order to increase the rate of electromigration, which depends sensitively on the mobility of the atoms. However, achieving an applied Joule heating that can be used to help controllably electromigrate atoms without causing catastrophic runaway is non-trivial.
Memristor devices are presented in this document containing a feedback configuration. The memristors consist of conductors which are stable in at least two states which can be accessed through the application of an applied voltage and current. The applied voltage and current induce migration of material within the memristor which changes its state. This effect can be used to store non-volatile memory. The feedback included in this configuration permits a specific voltage to be applied directly across a nanowire which allows it to be reproducibly switched between states and prevents thermal runaway breakdown of the memristive device. This configuration can be implemented with a single component nanowire and electrode geometry.
Advantageously, the feedback system of the current document permits precise and controllable Joule heating to the nanowire memristive element without thermal destruction of the device. The current feedback system also permits consistent voltage application to all nanowire memristive elements in applications where a plurality is utilized. This consistent voltage application, regardless of physical changes occurring in the memristive elements, could result in significant improvements to device performances, reproducibility among nominally identical memristive elements, and lifetime.